The present invention relates to polyamides which are advantageous as a binder for a thermosensitive image transfer recording medium, and a thermosensitive image transfer recording medium using the same.
Generally, there is known a thermosensitive image transfer recording medium, which is called an ink ribbon. This thermosensitive image transfer recording medium is constructed in such a manner that a thermofusible ink layer comprising as the main components a coloring agent and a binder comprising a wax and/or a low-melting point resin is formed on a heat-resistant support such as a polyester film and a polyamide film. Furthermore, a release layer comprising a wax may be interposed between the support and the thermofusible ink layer when necessary.
By use of the above thermosensitive image transfer recording medium, a thermosensitive image transfer recording method is currently widely employed. According to this thermosensitive image transfer recording method, the thermofusible ink layer of the thermosensitive image transfer recording medium is melted with application of heat by a thermal head and an ink composition of the thermofusible ink layer is imagewise transferred to a recording sheet, such as a sheet of paper and a film, which sheet is superimposed on the thermosensitive image transfer recording medium, opposite to the thermal head with respect to the recording medium.
The thermosensitive image transfer recording method has the advantages that the recording apparatus therefor is compact in size, relatively cheap and maintainable, and this method is capable of yielding images steadily and quietly.
However, conventional thermosensitive image transfer recording media cannot realize excellent thermal image transfer performance and fixing performance of images and cannot yield images with a satisfactory resolution and clearness when high-speed printing is conducted.
The conventional thermosensitive image transfer recording medium comprising a thermofusible ink layer in which a wax is used as a binder has high thermosensitivity to the heat of the thermal head. Accordingly, the thermofusible ink layer of this thermosensitive image transfer recording medium is swiftly melted with application of heat by the thermal head and the ink composition is imagewise transferred readily to a recording sheet even when the high-speed recording is carried out, in which heat application time is very short. This thermosensitive image transfer recording medium, however, has the shortcomings that the obtained images are blurred and easily peel off the recording sheet because the fixing property of the images to the recording sheet is insufficient.
In contrast to this, when the conventional thermosensitive image transfer recording medium comprising a thermofusible ink layer in which any of styrene--butadiene copolymer, vinyl chloride--vinyl acetate copolymer, ethyl cellulose and polyvinyl butyral, the melting point for which is in the range of 60.degree. C. to 110.degree. C., is used as a binder, it has the shortcomings that the thermal image transfer performance of the thermofusible ink layer is very poor.
The thermosensitive image transfer recording medium comprising a thermofusible ink layer in which the combination of the above-mentioned wax and low-melting point resin is used as a binder can improve the conventional shortcomings to some extent. However, there is no thermosensitive image transfer recording medium which can solve all of the above-mentioned shortcomings.